Generally, trunking can be thought of as a means of providing bandwidth aggregation between two points in a network (e.g., between two network devices). FIG. 1 is useful for illustrating the concept of trunking. A first device 105 and a second device 110 are connected through a plurality of physical network links 115-117. The first device 105 and the second device 110 may be network devices, such as a server, client, repeater, bridge, router, brouter, switch, or the like. The first device 105 includes ports 106-109 and the second device 110 includes ports 111-114. The ports provide the device with access to the attached network link by implementing appropriate network protocols such as the Ethernet protocol.
In this example, the physical network links 115-117 have been combined to form one logical channel, a "trunk" 140, between the first device 105 and the second device 110. As mentioned above, a trunk may provide increased bandwidth between two points in a network. For example, if links 115-117 each individually have a bandwidth of 100 Mbps, the resulting bandwidth of the trunk 140 is the sum of the bandwidths of the individual links (100 Mbps+100 Mbps+100 Mbps=300 Mbps).
At this point, it is important to recognize that two types of network devices have emerged. The first type of device (hereinafter "MODE 1 device") has the same media access control (MAC) address on its trunked ports. The second type of device (hereinafter "MODE 2 device") has a different MAC address on each trunked port.
One limitation of conventional switches is the fact that they are unable to perform upstream load balancing for MODE 1 devices. For example, assuming ports 106-108 of the first device 105 each use the MAC address of the first device 105, the second device 110 will relearn the location for that MAC address each time the first device 105 transmits a packet over a different trunked port 106-108. Consequently, packet trrric destined for the first device 105 over trunk 140 cannot be distributed over the ports 111-113. Rather, the port on which the second device 110 will transmit these packets depends upon which of the ports 106-108 transmitted last.
Based on the foregoing, it is desirable to implement a set of trunking rules relating to learning, forwarding, looping, and load balancing that are compatible with network devices operating in either MODE 1 or MODE 2. Also, in order to avoid introducing delays in packet transmission, it is desirable to update packet forwarding decisions that will be affected by trunk processing on-the-fly.